Summary Mild TBI related to deployment in the Middle East is rampant among our soldiers. The RAND Corporation has estimated that 320,000 of our soldiers may have experienced at least mild TBI. Even in mild TBI, which accounts for 80% of all TBI cases, causes damage to the brain that results in significant behavioral and cognitive changes. Veterans often report changes in personality, including irritability and aggression, loss of memory and loss of effectiveness. These problems are often permanent. The diagnosis of mild TBI is very challenging because there are no grossly evident neurological findings, like paralysis. The diagnosis of mild TBI is also complicated because this disorder frequently occurs together with the symptoms of post-traumatic stress disorder (PTSD), which include anxiety and depression, which are present in 44 and 27%, respectively, in soldiers with mild TBI. PTSD and depression can independently degrade cognitive and behavioral performance, and they can both exacerbate both the subjective complaints and objective cognitive deficits in mild to moderate TBI. Consequently, these psychological factors can be difficult to separate from the consequences of physical injury to the brain itself. This tangle of factors substantially increases the risk of diagnostic imprecision, particularly when purely subjective reports is used to assess the state of psychological health. Failure to establish the correct profile of disabilities leaves affected soldiers without a full explanation for their disabilities and hinders appropriate delivery of medical care. This proposal seeks to develop a new and portable eye movement test that has the potential to provide an objective method to diagnose TBI. There is substantial evidence that this type of eye movement test will prove especially valuable in the diagnosis of the milder cases of TBI which could otherwise go unrecognized. This battery of eye movement tests will be given to control subjects and veterans who have been diagnosed with TBI by the Neuro-Cognitive scientists at the Boston VA. The clinical study that is proposed in this grant seeks to determine the degree to which this new test predicts the presence of TBI and the severity of exposure to blasts. Given the opportunity to develop this new test instrument, our long-range goal is to use this new and portable eye movement test as a screening tool that would be administered pre-deployment at the same time as other basic medical examinations are being given. The same test would then be given post-deployment for those soldiers who were exposed to a blast. Certain differences in the pre- vs. post-deployment test might provide an objective parameter to corroborate a clinical diagnosis of blast- induced TBI.